Compressor capacity control



y 8, 1965 D. N. SHAW 3,184,151

COMPRESSOR CAPACITY CONTROL Filed May 31, 1962 2 Sheets-Sheet l INVENTOR. DAVID N. SHAW.

ATTORNEY.

y 13, 1965 o. N. SHAW 3,184,151

COMPRESSOR CAPACITY CONTROL Filed May 31, 1962 2 Sheets-Sheet 2 INVENTOR. 4 DAVlD N. SHAW.

FIG. 4 I I BY Maya/M ATTORNEY.

United States Patent 0 3,184,151 COMPRESOR CAPAQETY CONTROL David N. Shaw, Liverpool, N.Y., assignor to Carrier Corporation, Syracuse, N .Y., a corporation of Delaware Filed May 31, B62, Ser. No. 198,854- ltl Claims. (Cl. 230-31) This invention relates to a fluid compressor and to a method of controlling the capacity of the compressor, more particularly, to a refrigerant compressor having improved mechanism for controlling the capacity of the compressor and for reducing the cycling of the compressor during load fluctuations and to a method by which the capacity of a reciprocating compressor may be controlled responsive to pressure differences.

In a fluid compressor designed to operate at relatively constant speed, the load on the system in which the compressor is arranged may sometimes vary resulting in ineflicient operation of the compressor unless the capacity of the compressor can be varied to comply with the system variations.

One of the methods for varying the capacity of a reciprocating compressor operating at constant speed is to provide means for bypassing some or all of the cylinder entrapped vapor back to the suction side of the compressor from some point in the cylinder or the discharge manifold. On multi-cylinder compressors a variable capacity has been achieved by bypassing the full discharge of certain of the cylinders back to the suction side of the compressor. In a four cylinder compressor, one pair of cylinders may be manifolded together and arranged to deliver to the discharge side of the compressor at all times. The other pair of cylinders is manifolded together and arranged to discharge to the suction side of the compressor or to the discharge side of the compressor according to the load. Suitable controls responsive to the load imposed on the compressor are normally employed. Thus, a capacity reduction of fifty percent is possible with a four cylinder compressor when one pair of cylinders is unloaded. Similarly in a six cylinder compressor which operates with three cylinders in pairs, the discharge of only one pair of cylinders may be directed to the suction side of the compressor to eiiectuate a one-third reduction in capacity or two pairs of cylinders may be directed to the suction side of the compressor to effectuate a two-thirds reduction in capacity.

In some applications it has been found that present capacity control arrangements generally do not provide one hundred percent capacity when the compressor is fully loaded, as is desired. Further, there was a desire to replace the two-way and three-way solenoid valves often used in present bypass capacity control arrangements with a simpler, less expensive control arrangement.

An object of the present invention is to provide a refrigerant compressor having an improved capacity control in which the disadvantages and deficiencies of prior constructions are obviated.

Another object of the present invention is an improved method of controlling a multi-cylinder compressor by loading and unloading one or more cylinders in response to changes in load demand on the compressor whereby the capacity of the compressor is adjusted to meet changes in compressor load.

Another object of the present invention is to provide a compact, improved cylinder bypass type capacity con- 3,l8d,l5l Patented May 18, 1965 trol arrangement for unloading one or more cylinders of a refrigerant compressor.

A further object of the present invention is to provide a cylinder bypass type capacity control arrangement including a discharge side bleed arrangement responsive to compressor load to effectuate capacity control.

A still further object of this invention is to provide an apparatus for capacity control of a fluid compressor that is compact, less expensive and more reliable than present controls. Other objects of the invention will be readily perceived from the following description.

This invention relates to a reciprocating compressor comprising a first cylinder, a second cylinder, at discharge manifold, the first cylinder being in communication with the discharge manifold, a first path placing the second cylinder in fluid flow communication with the discharge manifold, a second path of fluid flow between the discharge port of the second cylinder and the suction manifold of the second cylinder, pressure actuated means for opening and closing the second path, a third path of fluid flow between the discharge manifold and the suction manifold of the second cylinder, a portion of the third path communicating with said pressure actuated opening and closing means, and means responsive to load conditions to vary the fluid pressure in the third path whereby an increase in load increases fluid pressure in the third path to close the second path and a decrease in load decreases fluid pressure in the third path to open the second path.

This invention further relates to a method of unloading a cylinder of a reciprocating compressor, in which the steps consist in placing the discharge and suction sides of the cylinder in communication to thereby unload the cylinder in response to a predetermined first discharge pressure, increasing the predetermined first discharge pressure in response to a predetermined first suction pressure, preventing communication between the dis charge and suction sides of the cylinder to load the cylinder at a second predetermined discharge pressure, and changing the second predetermined discharge pressure to the predetermined first discharge pressure in response to a predetermined second suction pressure whereby the discharge and suction sides of the cylinder are placed in communication to unload the cylinder.

The attached drawing illustrates a preferred embodiment of my invention, in which FIGURE 1 is a cross-sectional view of a four cylinder compressor including the apparatus of the present invention;

FIGURE 2 is a view partly in section and partly in elevation of a portion of a compressor including the apparatus of the present invention, the components of the capacity control being shown in the unloaded condition;

FIGURE 3 is a view partly in section and partly in elevation of'a portion of the compressor including the apparatus of the present invention, the components of the capacity control being shown in the loaded condition; and

FIGURE 4 is an enlarged view of a modified control valve arrangement.

Referring to FIGURE 1 of the drawing, a compressor 1d embodying the capacity control of the present invention is shown. The compressor 10 is a four-cylinder compressor having cylinder banks 3 and a. Each of the cylinder banks 3 and 4 includes a pair of cylinders 11 .discharged from the respective cylinders.

having pistons 14 disposed therein. Pistons 14 are con nected to the crankshaft by connecting rods 6. V

A suction manifold 22 is provided for introducing low pressure gas into the respective cylinders. A discharge manifold 23 is provided for receiving the pressurized gas Discharge manifold 23 is provided with an outlet 7 In the compressor 10, cylinder bank 3 is provided with a discharge manifold check valve 24 to be more fully described hereinafter. Cylinder bank 3 is also provided with a capacity control 40 of the present invention to be more fully described hereinafter.

While compressor 10 is shown as a four cylinder compressor having two banks of paired cylinders 3 and 4, it is understood that additional cylinder banks may be provided, some or all of which may be provided with capacity controls. For example, a six-cylinder compressor having three banks of paired cylinders may be envisioned wherein two of the three pairs of cylinders may be capacity controls constructed according to the presentinvention. In this manner, a one-third and a two-thirds reduction in capacity of the six cylinder compressor may be effected.

Referring particularly to FIGURES 2 and 3 of the drawing, the cylinder 11 includes a cylinder head 12 secured to the compressor 10 by bolts 13. The piston 14 is disposed within the cylinder 11 and moves therein. A valve plate 15 is placed between the cylinder head 12 and the compressor 19. Cylinder head gasket 17 and valve plate gasket 16 are disposed on opposite sides of valve plate 15 to prevent the escape of pressure from within the compressor. The cylinder communicates with the cylinder head through the discharge port 18 and suction port 19 in the valve plate 15.

Affixed to the valve plate are a discharge valve 20 and a suction valve 21. On the suction stroke of the piston, gases are drawn into the cylinder through the suction. port 19 and chamber 32 from the suction manifold 22. On the discharge stroke the compressed gas is forced into the discharge chamber 29 through the discharge port 18. When the cylinder is in loaded condition, the cylinder discharge pres-sure will force open the discharge piston check valve 24 to permit the passage of the refrigerant gas into the discharge manifol-d 23. Check valve 24 is urged toward closed position by spring 26 disposed between valve 24 and support 25. a 7

Within the cylinder head is a partition means 27 which divides the head into a discharge chamber 29 and a suction chamber 30. The chambers 29 and can 'be considered to be merely extensions of the discharge manifold and the suction manifold, respectively. The partition Lil.

. chamber47. A valve seat 57 is provided between the enlarged chamber 46 and the reduced chamber 47. Recip rocable valve 55 is positioned within the enlarged valve chamber 46. Stem 56 on valve 55 extends through reduced valve chamber 47 and the outer portion of the control body 45 to the outer extremity thereof. Valve 55 is provided with surface 59 adapted to engage valve seat 57 to thereby seal reduced valve chamber 47 from enlarged valve chamber 46. A valve spring 58 urges valve 55 toward valve seat 57.

Guide 36 is attached to the lower end of control body 45 and delimits the end of enlarged valve chamber 46.

' Guide 36 is provided with a central bore 48 communicatmeans 27 includes a wall 28 having an opening 33 to place the chambers 29 and 30 in communication with one another and a Wall 31 defining the chamber 32. Chamber 32 is placed in communication with suction manifold 22 ta-ining ring 37 secured to piston 34 and the other end engages retaining lip 38 of the guide 3 6.

As described heretofore, valve piston 34 is urged by spring 35 toward an open, that is, cylinder unloaded position. To-control closure of valve piston 34 to load the cylinder a control assembly 40 is provided. The body '45 of the control assembly 41) to secured to the cylinder head 12 by suitable means, such as bolts 41. Control assembly gasket 42 is provided between the cylinder head 12 and the control assembly body 45 to prevent the leakage of the gases from the compressor.

Control assembly 41} consists of a control body 45 having an enlarged valve. chamber ed and a reduced valve 'trol assembly body 45. One end of spring 35; abuts re- 7 ing enlarged valve chamber 46 with piston chamber 39.

A bleed passage 51 communicates enlarged valve chamber .6 with discharge passage 52. Cylinder head passage 53 communicates discharge passage 52 with discharge manifold 23. interconnecting suction manifold passages 49 and 51) in the cylinder head 12 and the control assembly body 45 respectively communicate reduced valve chamber 47 with the suction manifold 3%.

A diaphragm assembly is attached to the outer end of the control body 45 by suitable means such as threads 76. Diaphragm assembly 65 includes diaphragm 66 abutting the end of valve stem 56. A spring 67, acting through diaphragm 66 and valve stem 56, urges valve 55 in an open, that is, cylinder unloaded position. Spring '67 is capable of overriding valve spring 58. Screw 68 is provided for the purpose of adjusting the bias of spring 67. A diaphragm chamber 69 is provided in control body 45. Restricted orifice 7t) communicates diaphragm chamber 69 with suction manifold passage 51).

In the embodiment shown in FIGURE 4 a detent structure for valve 55 is shown. Valve stem 55 is provided with two recesses 72 in the outer circumference thereof corresponding to open and closed positions respectively of valve 55. Ball 71, located in control body 45, is adapted to cooperate with one or the other of the recesses 72 to releasably maintain valve 55 in open or closed position. Spring 73 urges ball 71 into engagement with one or the other of recesses 72. Screw 74 is provided to adjust the bias of spring 73. While the detent means has been shown as cooperating with valve stem 55, it is understood that the detent means may be provided on the valve 55 itself. 5' Considering the operation of the apparatus, on the suction stroke of the piston the gas enters the cylinder 11 from the suction manifold 22, through chamber 32, through the suction port 19 and past suction valve'21. On the discharge stroke of the piston the cylinder suction valve 21 is closed and the gas is forced through discharge 'portis and discharge valve 213 into the discharge chamber 29. From the chamber 29, the gas flows by the check valve 24 into the discharge manifold 23 for discharge through discharge outlet 7. Inasmuch as at least one of the other cylinders is loaded at all times, a suitable pres sure head is maintained in the discharge manifold 23. It is noted that check valve 24 is urged toward a closed position by spring 26. When the cylinder is loaded, that is, opening 33 is closed by control piston 34, the discharge pressurecf the loaded cylinder forces check valve 24 open to discharge pressurized gas into the'manifold 23. At all others times, check valve 24- is closed. The purpose of check valve 24- is to prevent pressurized gas in discharge manifold 23 from flowing into the suction manifold 3% while permitting the pressurized gas obtained from the cylinder during the loaded condition thereof to discharge into thedischarge manifold 23.

During the unloaded condition, that is, when valve 55 7 communicates the reduced valve chamber 47 with enlarged valve chamber 46, the reduced exhaust pressure,

in piston chamber 3? is ins'tifiicient to overcome spring 35 and, therefore, the control piston 34h; retracted and the cylinder is. unloaded due-to thecommunication of discharge chamber 29 with suction chamber 36 by means of opening 33. Reduction in discharge pressure in the piston chamber 39 is effected by bleeding the refrigerant gas from the discharge manifold 23 into the suction manifold 36 through bleed passage 51. The pressure of the discharge gas is reduced because the rate of bleed through the suction passages 4 51 is more than the rate of supply in the bleed passage 51 due to the restricted orifice thereof. This reduced pressure is insufficient to overcome the spring 35 which maintains control piston 34 in retracted position. Discharge pressure in the discharge manifold 23 (from the working cylinders) will close discharge check valve 24 isolating the compressor discharge manifold from the individual unloaded cylinder manifolds.

An increase in load on the compressor is reflected by an increase in pressure in the suction manifold 3%}. Diaphragm chamber 69, communicating with suction manifold 39 via passages 4?, 5i) and 7t? reflects a similar pressure increase. The increase of pressure in chamber 69 moves diaphragm (:5 against spring 67 whereby valve 55, under the influence of valve spring 5%, moves toward closed position. The increase in suction manifold pressure required to overcome spring 67 may be varied by adjustment of screw 63. As valve 55 moves toward closed position, the rate of bleed of discharge gas into the suction manifold passage 59 through bleed passage 51 decreases thereby resulting in an increase in pressure in enlarged valve chamber 46, passage 48, and piston chamber 34. It is understood that the position of valve 55 controls the rate of bleed, the rate of bleed decreasing as valve 55 moves toward closed position.

The increased pressure in enlarged valve chamber d6, acting on the lower surface of valve 55, speeds up closing movement of valve 55. As valve 55 closes, the rate of bleed is correspondingly reduced. The pressure accordingly builds up in areas 46, 48 and 39. As valve 55 approaches closed position, the increased pressure in areas 46, 48 and 39 moves control piston 34- against the urging of spring 35' to close bypass 33 thereby loading the cylinder. Surface 59 of valve 55 contact surface 57 of control body 45 thereby sealing enlarged valve chamber as from reduced valve chamber 47. Upon the closing by valve 55 of the bleed communication between the discharge manifold 23 and the suction manifold 38, the pressure in areas 46, and 39 equalizes with that of the discharge manifold 23.

A decrease in load is evidenced by a decrease in pressure in suction manifold 39. Diaphragm chamber 69, communicating with the suction manifold 30 by means of interconnecting passages 49, 5t and 7t reflects a similar decrease. The diaphragm 66 in response to this decrease, moves valve 55 open upon a predetermined pressure drop. As valve 55 opens, pressurized gas in areas as, 43 and 39 is bled around valve 55 through reduced valve chamber 47 into the suction passage 50. Although the initial opening of valve 55 is slight, the rate of bleed is rapid due to the pressure dirrerential between valve chambers 46 and 47, and due to the large elfective area of the port of the reduced valve chamber 47. Accordingly, the pressure in enlarged valve chamber 46 rapidly decreases, this decrease speeding up opening movement of valve 55. The speeded up opening movement of valve 55 causes rapid pressure drop in chambers as, 48 and 39 whereupon control piston 34, under the urging of spring 35, moves to open bypass 33 thereby unloading the cylinder. As valve 55 approaches fully open position, diaphragm 66 abuts the upper surface of control body 45, which serves as a stop therefor. Further opening movement of valve 55 is restrained by valve spring 58. With the establishment of equilibrium reduced pressure is maintained in chamber 39 whereby control piston 34 is held in retracted position.

Orifice '75 communicating diaphragm chamber 69 with suction manifold passage 5%), serves to prevent any rapid surge of pressure, such as occurs during opening movement of valve 55, from affecting diaphragm 66. As explained heretofore, during initial opening of valve 55, the high pressure in areas 46, 43 and 3h bleeds around valve 55 into reduced valve chamber area 47 into suction passage Sit. This bleeding is rapid, resulting in a surge of pressure in suction passage 50. The restricted size of orifice 7t) effectively prevents this pressure surge from aiiecting diaphragm 66.

The operation of the embodiment shown in FIGURE 4 is the same as disclosed in connection with FIGURES l3. With the control valve 55 open, as shown in FIG- URE 4, an increase in load on the compressor is reflected by an increase in pressure in suction manifold 36, passages 49, 50 and '70, and diaphragm chamber 69. This increased pressure moves diaphragm 66 against spring 67 permitting control spring 58 to overcome the detent effected by cooperating ball 71 and recess 72 to move control valve 55 toward closed position. With control valve 55 closed, a decrease in load is reflected by a decrease in pressure in suction manifold 3i passages 49, S9 and 7t and diaphragm 69. This decreased pressure moves diaphragm 6d against valve stem 56 to overcome the detent eliected by cooperating ball 71 and recess 72 to open control valve 55 to unload the compressor.

In the embodiment of FIGURE 4, the pressure required to load and unload the compressor is influenced by the adjustment of spring 6'7 through screw 68 and by the adjustment of detent spring '73 through screw 74.

While I have described a preferred embodiment of the invention, it will be understood that the invention is not limited thereto, since it may be otherwise embodied in the scope of the following claims.

I claim:

1. In a reciprocating compressor the combination of a cylinder including a movable piston therein, a suction manifold, a discharge manifold, a cylinder head for the compressor, said cylinder head including a partition separating a discharge chamber from a suction chamber, aid partition having an opening therein, normally open pressure actuated means for closing said partition opening, a bleed passage communicating said discharge manifold with said pressure actuated means and said suction manifold, means for controlling the pressure in said bleed passage including means to regulate flow through said bleed passage, and means responsive to changes in suction manifold pressure to actuate said flow regulating means to control pressure in said bleed passage including a pressure powered operator engageable with said flow regulating means, whereby upon a predetermined increase in suction pressure said operator actuates said flow regulating means to decrease flow through said bleed passage so that said pressure actuated means closes said partition opening to load said compressor, and upon a predetermined decrease in suction pressure said operator act-uates said how regulating means to increase flow through said bleed passage so that said pressure actuating means opens said partition opening to unload said compressor.

2. Apparatus according to claim 1 including detent means to releasably retain said flow regulating means in flow increasing and decreasing positions.

3. In a reciprocating compressor, the combination of a cylinder including a movable piston therein, a suction manifold, a discharge manifold, a cylinder head for the compressor, said cylinder head including a partition separating a di charge chamber from a uction chamber, said partition having an opening therein, pressure actuated means comprising a piston for closing said partition opening, means biasing said piston to open aid partition opening, a bleed passage communicating said discharge manifold with said pressure actuated means and said suction manifold, means for controlling the pressure in said bleed passage including a control valve adapted to regulate flow through said bleed passage, and means responsive to a predetermined change in suction manifold pressure to effect movement of said control valve including a pressure act-u- 7 ated operato-r engageable with said control valve and an orifice communicating said pressure actuated operator wit-h said suction manifold whereby, upon a predetermined increase in suction pressure, said pressure actuated operator moves said control valve to decrease flow through said bleed passage to actuate said piston to close said partition opening to load said compressor and, upon a predetermined decrease in suction pressure, said pressure actuated operator moves said control valve to increase flow through said bleed passage to actuate said piston to open said partition opening to unload said compressor.

4. Apparatus according to claim 3 including means for maintaining said control valve in open or closed position.

5. Apparatus according to claim 4 wherein said maintaining means includes detent means comprising at least one recess in said control valve corresponding to control valve increased or decreased regulating position, and an adjustable spring biased ball means cooperating with said recess to releasably maintain said control valve in position.

6. In combination with a reciprocating compressor having a cylinder including a movable piston therein, a suction manifold, a cylinder head, a discharge manifold, a

,partition in said cylinder head including an opening for communicating said discharge manifold with said suction manifold whereby said cylinder is unloaded, means responsive to discharge pressure for closing said opening, means for controlling the pressure imposed on said closing means including a restricted passage communicating said discharge manifold with said discharge pressure responsive closing means and said suction manifold whereby said discharge pressure at said discharge pressure responsive closing means is reduced, control valve means in said passage, pres-sure actuated means including a restricted orifice engageable with said control valve means and responsive to a predetermined increase in suction pressure to move said control valve means toward a closing posi tion to apply discharge pressure to said closing means whereby 'said partition opening is closed to load said cylinder.

7. In combination with a reciprocating compressor having a cylinder including a movable piston therein, a uction manifold, a cylinder head, a discharge manifold, a partition in said cylinder head including an opening for communicating said discharge manifold with said suction manifold whereby said cylinder is unloaded, pressure actuated'reciprocating piston means adapted to selectively close said opening, said piston means being biased toward open position and including a pressure chamber, a first restricted passage communicating said discharge manifold with said pressure chamber whereby said discharge pressure is applied to said pressure chamber, said discharge pressure being sufiicient to move said piston means against said bias'to close said opening to load said cylinder, and means for reducing said dischargepressure'in said pressure chamber including a second passage communicating said suction manifold and said pressure chamber whereby said discharge pressure i reduced to permit said piston'rneans to open said opening and unload said cylinder, valve means for controlling flow through said second passage, and diaphragm means including a restricted orifice, said diaphragm means being engageable with said valve means andradapted in response to an increase in suction pressure to actuate said valve means to decrease flow through said second passage whereby' aid discharge pressure moves said piston means to close said opening to loadsaid cylinder.

8. In a reciprocating compressor, the'combination of a'cylinder having a movable piston therein, a'suction chamber communicating with the cylinder, a discharge chamber communicating withtthe cylinder, means for" placing the suction chamber in communication with the discharge chamber to unload the cylinder, meansfor clos- 7 ing said communication means including a member movable in one direction responsive to discharge pressure and yieldable means for moving said member in the opposite direction and means for controlling movement of said member, said control means including a first passage through which discharge pressure is applied against said movable member, 'a bypass passage communicating with the first passage and the suction manifold, and means for preventing communication between the first passage and the bypass passage, said communication preventing means including a closure and a pressure responsive member to move said closure in one direction, a pressure chamber adjacent said pressure responsive member, a restricted passage placing the chamber in communication with the bypass passage whereby pressure in the bypass passage is reflected in the chamber, and yieldable means opposing the pressure applied against the pressure responsive member.

9. In a reciprocating compressor, the combination of a first cylinder having a movable piston therein, a second cylinder having a movable piston therein, a suction manifold communicating with said first and second cylinders, a first discharge manifold communicating with said first cylinder, a second discharge manifold communicating with said second cylinder and aid first discharge manifold, closure means for closing said second discharge manifold in response to a first discharge manifold pressure less than said second discharge manifold pressure, first means for placing the suction manifold in communication With said first discharge manifold whereby said first cylinder is unloaded, second means for preventing communication between the suction manifold and the first discharge manifold, said second means including a member movable in one direction in response to discharge pressure, yieldable means for moving said movable member in the opposite direction, and means for controlling movement'of said member, said movement controlling means including a first passage communicating with the second discharge manifold through which discharge pressure is applied against said movable member, a second passage communicating with the first passage and with the suction manifold, means for preventing communication 'between the first passage and the econd passage, said means including a closure member, a pressure responsive member to move said closure member, a pressure chamber adjacent the pressure responsive member, a restricted passage placing said chamber in communication with said second passage whereby pressure in the second passage is reflected in the chamber, and yieldable means opposing the pressure applied against the pressure responsive member.

10. In a reciprocating compressor, the combination of a cylinder including a movable piston therein, a suction manifold, a discharge manifold, a cylinder head for the compressor, said cylinder head including a partition ep arating a discharge chamber from a suction chamber, said partition having an opening therein, pressure actuated means comprising a piston for closing aid partition opening, means biasing said piston to open said partition opening, a bleed passage communicating said discharge manifold with said pressure actuated means and said suction manifold, means for controlling the pressure in said bleed passage including a control valve adapted to regulate flow through said bleed passage, and means including a restricted orifice responsive to a predetermined change in suction manifold pressure to effect movement of said control valve whereby, upon a predetermined increase in suction pressure, said moving means actuates said control valve to decrease flow through said bleed passage toactuate said piston to close said partition opening to load aid compressor and, upon' a predetermined decrease in suction pressure, said moving means actuates said'control valve to increase flow through said'bleed passage to actuate said piston to open said partition opening to unload said compressor, means for maintaining said control valve in open or closed position, said moving means including 1Q diaphragm means adapted to engage said control valve 7 References Cited by the Examiner means, first spring means acting on said diapi ragm means UNITED STATES PATENTS to bias said control means toward open posit-ion, second spring means acting on said control valve means in op- 21522762 9/50 Neeson 230-41 position to said first spring means, said first spring means 5 216731025 3/54 Liibus at 23031 normally overcoming said second spring means, whereby 2,7159% 8/55 Wilson 239-31 upon a predetermined increase in suction pressure, said 392L790 2/62 Brunson diaphragm moves against said first spring means to reduce 3,119,550 1/64 West 230-32 said first spring means bias to permit said second spring ROBERT M WALKER Prim Examiner means to move said control valve means toward closed 10 ry position. LAURENCE V. EFNER, Examiner. 

1. IN A RECIPROCATING COMPRESSOR THE COMBINATION OF A CYLINDER INCLUDING A MOVABLE PISTON THEREIN, A SUCTION MANIFOLD, A DISCHARGE MANIFOLD, A CYLINDER HEAD FOR THE COMPRESSOR, SAID CYLINDER HEAD INCLUDING A PARTITION SEPARATING A DISCHARGE CHAMBER FROM A SUCTION CHAMBER, SAID PARTITION HAVING AN OPENING THEREIN, NORMALLY OPEN PRESSURE ACTUATED MEANS FOR CLOSING SAID PARTITION OPENING, A BLEED PASSAGE COMMUNICATING SAID DISCHARGE MANIFOLD WITH SAID PRESSURE ACTUATED MEANS AND SAID SUCTION MANIFOLD, MEANS FOR CONTROLLING THE PRESSURE IN SAID BLEED PASSAGE INCLUDING MEANS TO REGULATE FLOW THROUGH SAID BLEED PASSAGE, AND MEANS RESPONSIVE TO CHANGES IN SUCTION MANIFOLD PRESSURE TO ACTUATE SAID FLOW REGULATING MEANS TO CONTROL PRESSURE IN SAID BLEED PASSAGE INCLUDING A PRESSURE POWERED OPERATOR ENGAGEABLE WITH SAID FLOW REGULATING MEANS, WHEREBY UPON A PREDETERMINED INCREASE IN SUCTION PRESSURE SAID OPERATOR ACTUATES SAID FLOW REGULATING MEANS TO DECREASE FLOW THROUGH SAID BLEED PASSAGE SO THAT SAID PRESSURE ACTUATED MEANS CLOSES SAID PARTITION OPENING TO LOAD SAID COMPRESSOR, AND UPON A PREDETERMINED DECREASE IN SUCTION PRESSURE SAID OPERATOR ACTUATES SAID FLOW REGULATING MEANS TO INCREASE FLOW THROUGH SAD BLEED PASSAGE SO THAT SAID PRESSURE ACTUATING MEANS OPENS SAID PARTITION OPENING TO UNLOAD SAID COMPRESSOR. 